1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device. More specifically, the present invention relates to an appearance improvement for zone backlit LCD devices and a method of reducing power consumption of an LCD device.
2. Discussion of the Related Art
In general, LCD devices are illuminated using various backlight devices. For example, light emitting diodes (LEDs) and fluorescent lamps (FLs), such as cold cathode fluorescent lamps (CCFLs) and hot cathode fluorescent lamps (HCFLs), are commonly used to provide light that passes through transparent substrates of the LCD devices. However, the backlight devices require significant amounts of power to produce the light for displaying images of a display panel of the LCD devices. Accordingly, a method of zone backlighting has been developed as a useful way for reducing power consumption in LCD devices. Using the zone backlighting method, power is reduced by shrinking the active image display region of the display panel. Thus, only the active image display region of the display panel requires illumination.
Using the zone backlighting method has many undesirable side effects including the creation of a halo border effect due to the low contrast ratio of the display panel. Specifically, when an image is produced on the display panel, elements of the backlight device outside of the active image display region are illuminated to ensure that the perimeter portions of the active image display region are of the same image intensity as a central portion of the active image display region. As a result, regions outside of the perimeter portions of the active image display region are illuminated and perceptually recognized to the eye of the viewer. Thus, since LCD pixels just outside of the active image display region may pass light due to light leakage, a halo border is generated along the perimeter of the active image display region distracting the viewer from the displayed images.
FIG. 1 is a reproduction of a display panel of an LCD device having a halo border effect for an LED zone backlighting according to the prior art, and FIG. 2 is a schematic plan view of an LED backlight device according to the prior art. In FIG. 1, the display panel 100 includes an active image display region 110 and a surrounding non-image display region 120. Accordingly, since the perimeter portions of the active image display region 110 must have same image intensity as the central portion of the active image display region 110, the LED elements of the backlight device outside of the active image display region 110 are illuminated. In FIG. 2, the LED elements 200a that would correspond to the perimeter portions of the active image display region 110 and the LED elements 200b that would correspond to the central portion of the active image display region 110 are powered to provide the same illumination intensity. Thus, as shown in FIG. 1, a halo border 130 is produced along the perimeter portions of the active image display region 110. As a result, image contrast is significantly reduced along the perimeter portions of the active image display region 110 due to the presence of the halo border 130. This reduced image contrast causes strain to a viewer's eye, thereby rendering the displayed images unpleasant to watch.
FIG. 3 is a reproduction of a display panel of an LCD device having a halo border effect for a fluorescent lamp FL (i.e, CCFLs or HCFLs) zone backlighting according to the prior art, and FIG. 4 is a schematic plan view of a FL (i.e., CCFLs or HCFLs) backlight device according to the prior art. In FIG. 3, the display panel 300 includes an active image display region 310 and a surrounding non-image display region 320. Accordingly, since the perimeter portions of the active image display region 310 must have same image intensity as the central portion of the active image display region 310, the FL elements of the backlight device outside of the active image display region 310 are illuminated. In FIG. 4, the FL backlight device 400 includes FL elements 410 that extend along an entire length L of the display panel 300 (in FIG. 3). Each of the FL elements 410 have end regions 420a that together with the outermost FL elements 410a would correspond to the perimeter portions of the active image display region 310 (in FIG. 3). In addition, the central regions 420b and the FL elements 410b would correspond to the central portion of the active image display region 310 (in FIG. 3). Accordingly, each of the FL elements 410 are powered to provide the same illumination intensity across the entire length L of the display panel 300 and within the active image display region 310 (in FIG. 3).
As shown in FIG. 3, since the FL elements 410 (in FIG. 4) extend along the entire length L of the display panel 300 outside the active image display region 310, a halo border 330 is produced along the entire length L of the display panel 300 and along a width W of the perimeter portions of the active image display region 310. As a result, image contrast is significantly reduced along the perimeter portions of the active image display region 310 due to the presence of the halo border 330. Moreover, the halo border 330 extends along the entire length of the display panel 300, thereby rendering images produced in the active image display region 310 unpleasant to view.
In addition, each of the LCD devices of FIGS. 1 and 2 unnecessarily consume a large amount of power to illuminate non-display regions of the display panels. Accordingly, a method is needed that significantly reduces the production of the halo border effect and reduces the unnecessary consumption of power to illuminate the non-image display region.